The decrease in time differences between the onset dates of menstrual flow in individuals who are in close contact are studied. Subjects include university students in the environment of dormitory or apartment living in groups of two, three, or four, and women working together, but not living together, in a city environment. The effects, if any, of the use of oral contraceptives are examined relative to hormonal changes. The cyclic release of pheromones involved with menstrual synchrony is also studied.